Field of Invention
The present invention relates to a crossing field between paper industry and insulation industry, and more particularly to a method for producing a meta-aramid fiber paper-based material.
Description of Related Arts
The meta-aramid fiber paper-based material is a whole-polyamide synthetic material which is prepared with raw materials of meta-aramid chopped fibers and meta-aramid fibrids through the wet-papermaking process and calendering process. Because of the high strength, the high modulus, the light weight, the flame retardancy, the high-temperature resistance, the corrosion resistance and the excellent dielectric property, the meta-aramid fiber paper-based material as the insulating material and the honeycomb core material is widely applied in the important fields of aerospace, rail transit and electrical insulation, and is the indispensable basic material of the modern industry.
As the important strategic reserve material and the high-tech material, the meta-aramid fiber paper-based material has been researched for a long time by experts and scholars. The American patent publication, U.S. Pat. No. 8,444,813, disclosed a method for preparing a meta-aramid fiber paper-based material, comprising steps of: adopting chopped fibers having a weight of 30-80% of a total absolute dry weight and fibrids having a weight of 20-70% of the total absolute dry weight as raw materials, forming a paper through an inclined wire forming machine with a wet-papermaking process, and, through two-stage drying, obtaining the meta-aramid fiber paper-based material. According to the Chinese patent application, CN200610043659.0, 5-95 wt % of the chopped fibers and 5-95 wt % of the fibrids were adopted as the raw materials; then, the meta-aramid fiber base paper was prepared through the wet-papermaking process; next, functional nanoparticles were precoated on the surface of the meta-aramid fiber base paper, and the precoated meta-aramid fiber base paper was processed with high-temperature calendering; and finally, the high-performance meta-aramid fiber paper-based material was obtained. According to the Chinese patent application, CN200510049055.2, at least one end surface of the meta-aramid chopped fibers was processed with fibril dividing, so that the specific surface area was increased; then, the processed meta-aramid chopped fibers were uniformly mixed with the meta-aramid fibrids; after forming a paper through the wet-papermaking process, the formed paper was processed with high-temperature calendering; and finally, the meta-aramid fiber paper-based material product having the excellent mechanical strength was obtained.
With the rapid development of science and technology, in the application process, the meta-aramid fiber paper-based material always faces tests of various bad working conditions, such as the high and low temperature, the high voltage, and the high light radiation, which puts forward higher and higher requirements on the overall performance, such as characteristics of surface smoothness, mechanical strength, dielectric property, and aging resistance, and the performance stability of the meta-aramid fiber paper-based material. Thus, for better meeting the development requirements of the modern industry, it is necessary to continuously adopt the new technology to improve the quality and the performance of the meta-aramid fiber paper-based material product.
Firstly, the meta-aramid fiber paper-based material is a photosensitive high polymer material, which is easy to be aged and degraded under conditions such as the ultraviolet irradiation and the high-temperature environment, and finally causes the yellowing paper and the great decrease of the overall performance. Moreover, because the meta-aramid fiber paper-based material is applied in the fireproof material, the flame retardancy thereof is required to be improved. The Chinese patent application, CN201110032074.X, disclosed a method for preparing an additive meta-aramid fiber paper-based material. During the preparation stage of the meta-aramid fibrids, the silica, the clay, the carbon black, the titanium oxide, the zirconium oxide, and the resin functional powders were added, which improved the aging resistance of the meta-aramid fiber paper-based material. However, the added functional powders always had the serious side effects on the mechanical performance of the fibers and the paper-based material thereof. Thus, it is required to develop a new additive system, which is able to improve the aging resistance and the flame retardancy of the meta-aramid fiber paper-based material, without generating any negative effect on the other useful performances.
Secondly, the meta-aramid fiber paper-based material is more and more applied in the high-strength lightweight honeycomb structure material, and thus the mechanical strength thereof is urgently required to be further increased. According to the Chinese patent application, CN200810134636.X, 0-19 wt % of the polyester fibers were added, and, after the wet-papermaking process and calendering, the meta-aramid fiber paper-based material was prepared, which greatly increased the mechanical strength thereof. However, the introduction of the third ingredient caused a great decrease of the performance of the meta-aramid fiber paper-based material, such as the high-temperature resistance and the flame retardancy, which limited the popularization and the application of the meta-aramid fiber paper-based material.
Next, the fluff problem exists on the surface of the meta-aramid fiber paper-based material, causing the burrs generating in the subsequent machining process such as dipping and paint spraying, thereby leading to the local concentration of the field intensity in the high-voltage environment and the instantaneous breakdown phenomenon, and seriously threatening the safe operation of the electrical equipment. Thus, the surface smoothness of the meta-aramid fiber paper-based material is required to be improved. The American patent publication, U.S. Pat. No. 5,622,775, disclosed a multi-layered papermaking technology. The surface layer consisted of 10-35% by weight of the chopped fibers and 65-90% by weight of the fibrids, and the inner layer consisted of 45-60% by weight of the chopped fibers and 40-55% by weight of the fibrids. Through processing with composite squeezing and drying, and finally with calendering, the meta-aramid fiber paper-based material having the high smoothness was obtained. However, to realize the multi-layered papermaking technology, the three-inclined-wire papermaking machine was required. Thus, the equipment requirement is relatively high, the production process is complex, and the production cost is high.
Finally, the demands on the thick (6-30 mil) meta-aramid fiber paper-based material in the electrical insulation field is bigger and bigger, while the related research reports of the thick meta-aramid fiber paper-based material are few. Because of the relatively high basic weight (150-700 g/cm2) of the thick meta-aramid fiber paper-based material, the conventional single-layer or multi-layer papermaking machine is difficult to meet the production requirements, and thus the production difficulty is relatively high. Conventionally, in the actual production of the thick meta-aramid fiber paper-based material, the multi-layer base paper dry pressing technology is generally adopted. However, blistering and delamination easily occur, and the interlayer bonding strength is relatively low. Meanwhile, the meta-aramid fiber paper-based material has the relatively bad performance stability, and the products from batch to batch and the products in the same batch have the relatively high performance fluctuation which are urgently required to be solved.